The Walls of Ba Sing Se

Defender
Other permanents you control have indestructible.

Bark of Doran

Equipped creature gets +0/+1.
As long as equipped creature's toughness is greater than its power, it assigns combat damage equal to its toughness rather than its power.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Meekstone

Creatures with power 3 or greater don't untap during their controllers' untap steps.

Doran, the Siege Tower

Each creature assigns combat damage equal to its toughness rather than its power.

Doran, Besieged by Time

Each creature spell you cast with toughness greater than its power costs {1} less to cast.
Whenever a creature you control attacks or blocks, it gets +X/+X until end of turn, where X is the difference between its power and toughness.